Re: grub-install fails with nbd device

[listsb]

i've managed to get thing working, sort of, but i still don't understand.

if i run kpartx against /dev/nbd0, it adds device nodes in /dev/mapper/, and 
i'm able to use those.  grub-install runs fine, and doesn't complain.  so for 
some reason, it seems to not like the device nodes in /dev/ - e.g. 
comparatively:

>l /dev/nbd*
brw------- 1 root root 43,   0 Jun 20 17:12 /dev/nbd0
brw------- 1 root root 43,   1 Jun 20 17:12 /dev/nbd0p1
brw------- 1 root root 43,   2 Jun 20 17:12 /dev/nbd0p2
brw------- 1 root root 43,  32 Jun 20 17:12 /dev/nbd1
[...]

>l /dev/mapper/nbd*
brw------- 1 root root 252, 7 Jun 20 17:12 /dev/mapper/nbd0p1
brw------- 1 root root 252, 8 Jun 20 17:12 /dev/mapper/nbd0p2

in both cases, it seems to me the kernel has awareness of the partitions, 
because i can work with them as expected in any other way [even without running 
kpartx], but there's something about the /dev/ nodes that i guess grub doesn't 
like.

why is this necessary?  what is it about the /dev/ nodes that grub doesn't like?

thanks
-ben

> On Jun 16, 2020, at 12.10, listsb <listsb-grub@bitrate.net> wrote:
> 
> hi-
> 
> i'm attempting to install grub to an esp partition on an nbd device, but it 
> fails, and says "error: cannot find a GRUB drive for /dev/nbd0p1" [see 
> below].  this is a qcow2 image, presented to the system as /dev/nbd0 [e.g. 
> qemu-nbd --connect ...].  i also have another "traditional" disk connected as 
> /dev/vdd, partitioned the exact same way, and this works as expected.
> 
> i've tried --force, --removable, --no-nvram, with and without device.map 
> files, using a loop device - all with the same result.
> 
> what makes grub decide it's not a grub drive?  also, why doesn't --force make 
> it work?  based on what the man page says, it seemed to me like it should.
> 
> here's some hopefully relevant info - thanks!:
> 
>> parted /dev/nbd0 print
> Model: Unknown (unknown)
> Disk /dev/nbd0: 1074MB
> Sector size (logical/physical): 512B/512B
> Partition Table: gpt
> Disk Flags:
> 
> Number  Start   End     Size   File system  Name  Flags
> 1      1049kB  105MB   104MB  fat32        esp   boot, esp
> 2      105MB   1073MB  968MB               pv1   lvm
> 
>> cat 
>> /opt/build/operating_systems/alpine/work/imagetest-c5676f32-412a-4ef4-b617-962b932b8ef2/boot/grub/device.map
> (hd0)                 /dev/nbd0
> 
> installing grub to /dev/nbd0p1:
> =============================
>> grub-install \
>>  --verbose \
>>  --force \
>>  --removable \
>>  --target=x86_64-efi \
>>  --bootloader-id=alpine \
>>  
>> "--efi-directory=/opt/build/operating_systems/alpine/work/imagetest-c5676f32-412a-4ef4-b617-962b932b8ef2/boot/efi"
>>  \
>>  
>> "--boot-directory=/opt/build/operating_systems/alpine/work/imagetest-c5676f32-412a-4ef4-b617-962b932b8ef2/boot"
> Installing for x86_64-efi platform.
> grub-install: info: cannot open 
> `/opt/build/operating_systems/alpine/work/imagetest-c5676f32-412a-4ef4-b617-962b932b8ef2/boot/grub/device.map':
>  No such file or directory.
> grub-install: info: /dev/nbd0p1 is not present.
> grub-install: info: Looking for /dev/nbd0p1.
> grub-install: info: /dev/nbd0 is a parent of /dev/nbd0p1.
> grub-install: info: /dev/nbd0p1 is present.
> grub-install: info: Looking for /dev/nbd0p1.
> grub-install: info: /dev/nbd0 is a parent of /dev/nbd0p1.
> grub-install: info: /dev/nbd0p1 is present.
> grub-install: info: Looking for /dev/nbd0p1.
> grub-install: info: /dev/nbd0 is a parent of /dev/nbd0p1.
> grub-install: error: cannot find a GRUB drive for /dev/nbd0p1.  Check your 
> device.map.
> 
> installing grub to /dev/vdd1:
> =============================
>> grub-install \
>>  --force \
>>  --removable \
>>  --target=x86_64-efi \
>>  --bootloader-id=alpine \
>>  
>> "--efi-directory=/opt/build/operating_systems/alpine/work/imagetest-1e909864-b820-4939-9dff-b4918184c632/boot/efi"
>>  \
>>  
>> "--boot-directory=/opt/build/operating_systems/alpine/work/imagetest-1e909864-b820-4939-9dff-b4918184c632/boot"
> Installing for x86_64-efi platform.
> File descriptor 4 (/dev/vdd1) leaked on vgs invocation. Parent PID 10249: 
> grub-install
> You have a memory leak (not released memory pool):
> [0x7fcace1b3f80] dtree
> Internal error: Unreleased memory pool(s) found.
> File descriptor 4 (/dev/vdd1) leaked on vgs invocation. Parent PID 10249: 
> grub-install
> You have a memory leak (not released memory pool):
> [0x7fcace1b3f80] dtree
> Internal error: Unreleased memory pool(s) found.
> Installation finished. No error reported.